Yeh, it's called google... Search "Port #" ie: "Port 25", it'll almost always spit out some result. Most Port Scanners (such as "SuperScan" come with their own portlist. No portlist will show every port or at least every use for every port.
In accordance with Dictionary.com
An applications programming interface (API) which activates network operations on IBM PC compatibles running under Microsoft's DOS. It is a set of network commands that the application program issues in order to transmit and receive
data to another host on the network. The commands are interpreted by a network control program or network operating system that is NetBIOS compatible. See NetBOLLIX.